1. Field of the Invention
The invention relates to protocol translation in a data storage system.
2. Background Art
Many computer peripheral devices are designed to attach directly to a computer system by way of a memory-mapped system interface such as PCI-Express. This approach works well for systems consisting of a small number of host processors and their directly-attached peripherals. However, this approach does not scale well to systems consisting of a large number of host processors possibly contained in many separate equipment racks interconnected with a large number of peripheral devices dispersed across multiple equipment racks. Furthermore, it is difficult to construct a fault-tolerant interconnect network among these components using only PCI-Express.
A more flexible and fault-tolerant interconnect technology such as InfiniBand is better suited for connecting a large cluster of computers and their peripherals in such a way that each computer can reach each peripheral device with low access latency and high composite data rate. However, simply attaching a peripheral device that is designed for local attachment using PCI-Express directly to an InfiniBand Host Channel Adapter (HCA) does not allow the computers to communicate with their peripherals because of the major differences between the memory access protocol used by PCI-Express and the Remote Direct Memory Access (RDMA) protocol used by InfiniBand.
What is needed is an efficient means of translating the memory access operations performed by the peripheral device into the RDMA interactions with the InfiniBand HCA that will cause it to carry out these memory access operations across the InfiniBand network.
Currently, the only way for a computer to access a PCI-Express peripheral device that is on the other side of an InfiniBand network is for the computer to communicate with a second computer that is directly connected to the peripheral device by PCI-Express and give the second computer directions to carry out the desired access on behalf of the initiating computer. This process introduces large delays in accessing the peripheral device. Furthermore, to sustain a high access rate using this technique requires the use of a fast (and therefore, expensive) computer that is directly attached to the peripheral device.